Method of forming a thermo pyrolytic graphite-embedded heatsink

ABSTRACT

The present disclosure is related to creating blocks of aluminum and/or copper material having embedded TPG elements for forming heatsinks. The metal blocks have an improved thermal conductivity in the X-Y plane. Furthermore, the TPG-embedded heatsinks can be created using methods capable of being performed using various machines and equipment in many various facilities.

BACKGROUND OF THE INVENTION

This disclosure relates generally to methods of forming thermo pyrolytic graphite (TPG)-embedded metal blocks to serve as heatsinks and, more particularly, to forming metal blocks of aluminum and/or copper material having TPG elements embedded therein to serve as heatsinks.

Modern embedded computer systems contain very high thermal power electrical components in a volumetrically constrained environment. The volumes typically do not change as the power dissipation of the components increase, presenting significant challenges in the management of component temperatures. In the past, a variety of direct cooling techniques such as active or passive heatsinks composed of high thermally conductive materials, such as aluminum and/or copper, have been used to manage rising temperatures. These materials, however, are only sufficient if a relatively large amount of surface area is presented to the airstream, necessitating a physically larger heatsink structure that occupies a large amount of the total available volume. As the physical size of the heatsink increases, the ability of the material to rapidly carry heat to the extremities of the heatsink, thereby exposing the heat to the airstream, is diminished.

Thermo Pyrolytic Graphite (TPG) materials have been found to have the ability to conduct heat in a single (X-Y) plane as compared to conventional metal materials. Furthermore, TPG has been found to have an improved overall conductivity as compared to copper. Recently, a method has been developed to embed TPG material into an aluminum structure using a diffusion bonding process. The diffusion bonding process, while resulting in a suitable thermal contact between the TPG material and the aluminum structure, has limitations in that specialized equipment is needed to create the TPG-embedded structures in a time-consuming process, resulting in an expensive product.

As such, there is a need for a method to create a cost-effective product having TPG embedded into a metal structure, such as an aluminum structure, to provide effective thermal conductivity in the X-Y plane. Additionally, it would be advantageous if the method were easily reproducible and could be performed in many various facilities using many various types of equipment.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method for forming a thermo pyrolytic graphite (TPG)-embedded heatsink is provided. The method includes suspending at least one TPG element in a form. The form is filled with a metal material and heated to bond the TPG element within the metal material. The bonded TPG-embedded metal material is cooled.

In another aspect, a method for forming a thermo pyrolytic graphite (TPG)-embedded heatsink is provided. The method includes obtaining a foam block. At least one TPG element is deposited into the foam block. The foam block with the at least one TPG element is deposited into a container, and the container is filled with molding sand. The foam block is filled with a molten metal material.

In another aspect, a method for forming a thermo pyrolytic graphite (TPG)-embedded heatsink is provided. The method includes separating a foam block into at least two portions. At least one TPG element is deposited between the at least two portions of the foam block. The at least two portions of the foam block are coupled together to form a single block with the TPG element. The single block with the TPG element is deposited into a container, and the container is filled with molding sand. The foam block is filled with a molten metal material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a method for forming a thermo pyrolytic graphite (TPG)-embedded heatsink according to a first embodiment of the present disclosure.

FIG. 2 is a schematic view of a foam block for depositing a thermo pyrolytic graphite (TPG) therein according to a second embodiment of the present disclosure.

FIG. 3 is a schematic view of the foam block of FIG. 2 having a TPG element deposited therein.

FIG. 4 is a schematic view of the foam block with the TPG element of FIG. 3 deposited within a container.

FIG. 5 depicts two portions of a foam block for depositing a thermo pyrolytic graphite (TPG) therein according to a third embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure is related to forming thermo pyrolic graphite (TPG)-embedded heatsinks and heatframes. As used herein, “TPG” refers to any graphite-based material in which the graphite is aligned in one direction for optimal heat transfer. The materials are typically referred to as “aligned graphite”, “TPG”, and “Highly Oriented Pyrolytic Graphite (HOPG)”. The TPG elements provide improved thermal conductivity in the X-Y plane of the metal blocks. Specifically, it has been found that by using the methods of embedding TPG elements into metal blocks as provided in the present disclosure, temperatures created during the use of electrical systems, such as computer systems, can be lowered by about 10° C. or more as compared to conventional thermal solutions. This improved temperature release allows for almost a doubling of the electrical systems' power capacity in the same volume environment. Furthermore, the increase in power may result in systems being supported that could not have otherwise been supported, or may allow existing systems to be used in environments having higher ambient temperatures.

In one embodiment, as depicted in FIGS. 1-3, at least one TPG element 10, 12 is held in form 20, to embed elements 10, 12 into a metal block (not shown) for use in a heatsink or a heatframe. The TPG elements 10, 12 are suspended in a form 20. The form 20 is filled at least partially with a metal material (not shown) and heated to bond TPG elements 10, 12 within the metal material. The bonded TPG-embedded metal material is then cooled to form a metal block including embedded TPG elements 10, 12 (i.e., a TPG-embedded heatsink).

TPG elements 10, 12 can be obtained using any suitable method and/or equipment known in the art for fabricating TPG elements and guided by the teachings herein provided. Alternatively, TPG elements 10, 12 can be obtained commercially from suppliers, such as Momentive Performance Material located in Wilton, Conn.

In one embodiment, as shown in FIG. 1, TPG elements 10, 12 are configured in a planar TPG strip. In a particular embodiment, TPG elements 10, 12 are planar TPG strips having 90 degree edges. Furthermore, while one or more dimensions of TPG elements 10, 12 may vary, TPG elements 10, 12 of one embodiment have a thickness of about 0.06 inches. While shown in FIG. 1 as in a planar strip, it should be understood by one skilled in the art that TPG elements 10, 12 may have any suitable configuration known in the art without departing from the present disclosure. For example, TPG elements 10, 12 can be configured in any suitable shape including, without limitation, an oblong or a triangular shape, and including, without limitation, intermediate holes to be filled with metal.

In one embodiment, TPG elements 10, 12 are plated with a metal-based coating material (not shown). More specifically, a layer of metal, such as aluminum, copper, iron, silver, gold, nickel, zinc, tin, or a combination thereof, is applied to an outer surface of TPG elements 10, 12. In a particular embodiment, the metal-based coating material is a copper coating material with a nickel overcoat.

The metal-based coating material suitably provides mechanical strength. The metal-based coating material is typically at least about 0.001 inches thick. More suitably, the metal-based coating material is applied to TPG elements 10, 12 in an amount of from about 0.0005 inches to about 0.002 inches and, even more suitably, the metal-based coating material has a thickness of from about 0.006 inches to about 0.025 inches.

The metal-based coating material can be applied to the outer surface of TPG elements 10, 12 in any pattern known in the art. For example, in one embodiment, the metal-based coating material is applied in a cross-hatched pattern. In an alternative embodiment, the metal-based coating material is applied in a striped pattern.

At least one TPG element 10, 12 is suspended in form 20. Form 20 can be any suitable form known in the art. Dimensions of form 20 depend at least partially upon the desired dimensions of the metal block (i.e., heatsink) to be formed.

As TPG elements 10, 12 are suspended, and as such, are “floating” within form 20, stresses experienced during high temperature heating processes, such as a soldering process as described below, can be avoided. Suitably, one or more TPG elements 10, 12 are suspended in form 20. More specifically, as shown in FIG. 1, two TPG elements 10, 12 are suspended in form 20. While shown in FIG. 1 as including two TPG elements 10, 12 suspended in form 20, it should be understood by one skilled in the art and guided by the teachings herein provided that less than two or more than two TPG elements 10, 12 may be suspended without departing from the scope of the present disclosure. For example, three TPG elements may be suspended in the form and, even more suitably, four or more TPG elements may be suspended in the form. Also, while shown in FIG. 1 as being in a particular orientation in the form, it should be understood by one skilled in the art and guided by the teachings herein provided that any orientation known in the art may be used.

In one embodiment, TPG elements 10, 12 are suspended in form 20 using at least one peg, such as respective pegs 30, 32. Suitably, pegs 30, 32 for suspending TPG elements 10, 12, respectfully, are metal pegs, such as pegs including steel.

Once TPG elements 10, 12 have been suspended within form 20, form 20 is at least partially filled with a metal material (not shown). In one embodiment, the metal material includes at least one of aluminum and copper. Both aluminum and copper have been shown to provide high conductivity when used in heatsinks. More specifically, as shown in FIG. 3, aluminum provides good thermal conductivity in a “Z” plane when used in heatsinks. However, as noted above, aluminum and copper alone fail to provide sufficient heat transfer in the X-Y plane and, as such, the present disclosure has combined TPG with at least one of aluminum and copper.

In a particular embodiment, the metal material is a powdered metal material. For example, the metal material may include powdered aluminum and/or powdered copper. In an alternative embodiment, the metal material includes a liquid or molten metal material, such as liquid aluminum and/or liquid copper.

In a particular embodiment in which a molten metal material is used, the molten metal material is introduced into form 20 using a suitable metal injection molding (MIM) process. Specifically, the metal material to be injected is heated above its liquidus temperature and then forced into form 20 (i.e., mold) by the extension of a piston in an injection chamber of the MIM equipment. In an alternative embodiment using a MIM process, the molten metal material is introduced into form 20 using a suitable thixotropic injection molding method. In this method, the metal is first heated to a thixotropic state rather than to a completely liquid state, and then injected into form 20 from an injection chamber. In this method, a screw rather than a piston is often used to inject the metal material into form 20. The piston and the screw contain a shaft portion, which is attached to a drive mechanism. The drive mechanism is typically a motor, however, hydraulic mechanisms have also been used.

When a powdered metal material is used to fill form 20, filled form 20 is then heated to bond TPG elements 10, 12 within the metal material. In a particular embodiment, TPG elements 10, 12 are heated using a sintering process. Generally, sintering strengthens the powdered metal material and normally produces densification and, in powdered metal materials, recrystallization.

Once bonded, form 20 containing the bonded TPG-embedded metal material is cooled to form metal block embedded with TPG (i.e., TPG-embedded heatsink). Generally, form 20 and the TPG-embedded metal material is stored in a suitable location until it reaches room temperature (approximately 24° C.).

In an alternative embodiment, as depicted in FIGS. 2-4, a metal block is impregnated with TPG using a lost form casting process. In this embodiment, a foam block 100 (shown in FIG. 2) is obtained. At least one TPG element 110 is deposited into foam block 100 (shown in FIG. 3). Foam block 100 with TPG element 110 is deposited into a container 200 (shown in FIG. 4), and container 200 is at least partially filled with molding sand (not shown) with sprues 130, 132 exposed. Molten metal material (not shown) is poured into the sprues, replacing the foam and forming the TPG-embedded block.

As described above, to begin the lost form casting process, foam block 100 is obtained. Suitably, with reference to FIG. 2, foam block 100 is made from a medium to high density foam. Typically, dimensions of foam block 100 will vary depending upon the desired heatsink.

In one embodiment, as shown in FIG. 3, at least one TPG element 110 is deposited in pre-cut slots 120 formed or defined within foam block 100. Typically, slots 120 are sized according to the TPG element 1 10. For example, in one embodiment, slots 120 are 6″×0.375″×0.60″. Slots 120 may have any shape known in the art suitable for use with TPG elements 1 10. In one embodiment, TPG elements 110 are similar to TPG elements 10, 12 described above. In one embodiment, TPG elements 110 are planar TPG strips such as described above and, as such, pre-cut slots 120 are rectangular openings sized to allow TPG element 110 to slide within foam block 100. While shown in FIG. 3 as being rectangular pre-cut slots 120 and planar TPG elements 110, it should be understood by one skilled in the art that TPG elements 110 can be any suitable shape known in the art (as described more fully above) and pre-cut slots 120 can be any complementary shape for allowing TPG elements 110 to be deposited therein without departing from the scope of the present disclosure. Furthermore, it should be understood by one skilled in the art that slots 120 may not be pre-cut, but may be formed by placing pre-heated TPG elements in the foam, allowing them to melt the foam, thereby, forming slot 120, or that TPG elements 110 may simply be wedged between two pieces of foam without departing from the scope of the present disclosure.

In an alternative embodiment, as shown in FIG. 5, foam block 100 includes at least two portions 300, 302. Foam block 100 may be separated into any suitable number of portions 300, 302 using any suitable equipment known in the art for separating foam material. First portion 300 and second portion 302 may be equal or may not be equal. For example, in one embodiment (not shown), foam block 100 is separated into first portion 300 and second portion 302, wherein second portion 302 is twice the volume of first portion 300. Moreover, foam block 100 may be separate into more than two portions 300, 302, for example, foam block 100 may be divided into three portions, four portions, or even five or more portions without departing from the scope of the present disclosure.

When foam block 100 is separated into portions 300, 302, TPG element 110 is deposited between portions 300, 302 and then portions 300, 302 are coupled to form a single foam block including TPG element 1 10. Portions 300, 302 may be coupled using any means known in the art for coupling foam materials. For example, in one embodiment, foam portions 300, 302 are coupled using any adhesive composition known in the adhesive art. In an alternative embodiment, portions 300, 302 are coupled using mechanical means, such as screws or rivets.

Referring back to FIG. 3, once TPG element 110 has been deposited within foam block 100, sprues 130, 132 are added to foam block 100. In one embodiment, foam block 100 with the sprues 130, 132 is dipped into a plaster (not shown) to form a hard shell around foam block 100. Typically, the plaster provides a smoother finish to an exterior surface of finished metal block that is formed out of foam block 100.

Now referring to FIG. 4, foam block 100, with or without a plaster shell, is deposited into a container 200 with spues 130, 132 located at a top 202 of the container 200. Sprues 130, 132 are used to provide entry for molten metal and to form exhaust vents for gasses that may form during the lost foam casting process.

In one embodiment, container 200 is a sand-filled container. Sand-filled container 200 facilitates retaining the form of the molten metal until the metal cools and solidifies.

Once foam block 100 has been deposited within container 200, molten metal material, such as the molten metal material described above, is poured into sprues 130, 132, vaporizing the foam and forming the TPG-embedded block. Generally, the molten metal material remains in container 200 until all of the foam of foam block 100 is depleted. This results in a metal block embedded with TPG elements 110 (i.e., TPG-embedded heatsink).

In one embodiment, metal block is further removed from container 200 and machined down in size for use as a heatsink.

In one embodiment, wherein metal block embedded with the TPG element 110 is created using sintering, metal injection molding, or lost foam casting, metal block is machine-configured to have heat fins (generally shown in FIG. 2 at 2, 4, 6, and 8). By including heat fins 2, 4, 6, 8, the surface area of the material that is thermally exposed to the surrounding environment is increased to facilitate heat dissipation. Typically, the thickness of heat fins 2, 4, 6, 8 are substantially identical, and distances between two adjacent heat fins 2, 4, 6, 8 are also suitably identical. However, it should be understood by one skilled in the art that while FIG. 2 shows heat fins 2, 4, 6, 8 having substantially identical thickness and substantially identical spacing, heat fins 2, 4, 6, 8 may have different thicknesses and/or vary spacing between heat fins 2, 4, 6, 8 without departing from the scope of the present disclosure. Heat fins 2, 4, 6, 8 in one embodiment are approximately 0.24 inches in height and approximately 0.024 inches thick, and the spacing between adjacent heat fins is approximately 0.096 inches.

In one embodiment, wherein the metal block embedded with TPG elements 110 is created using sintering, metal injection molding, or lost foam casting, the mold or foam block may be created to incorporate fins or other features prior to injection of molten metal in order to reduce or eliminate machining steps.

In another embodiment, wherein the metal block embedded with TPG elements 110 is created using sintering, metal injection molding, or lost foam casting, the mold or foam block may be created to incorporate more complex features prior to injection of molten metal to create conduction-cooled heatframes.

While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. 

1. A method for forming a thermo pyrolytic graphite (TPG) therein according to a first embodiment of the present disclosure-embedded heatsink, the method comprising: suspending at least one TPG element in a form; filling the form with a metal material; heating the form to bond the at least one TPG element within the metal material to produce a TPG-embedded heatsink; and cooling the bonded TPG-embedded heatsink.
 2. A method in accordance with claim 1, comprising suspending at least one planar TPG strip in the form.
 3. A method in accordance with claim 1, comprising suspending the at least one TPG element using a metal peg.
 4. A method in accordance with claim 1, comprising filling the form with a metal material selected from the group consisting of aluminum, copper, and combinations thereof.
 5. A method in accordance with claim 4, comprising filling the form with a powdered metal material.
 6. A method in accordance with claim 4, comprising filling the form with a liquid metal material.
 7. A method in accordance with claim 1, wherein filling the form comprises metal injection molding.
 8. A method in accordance with claim 1, wherein heating the form comprises a sintering process.
 9. A method in accordance with claim 1, further comprising plating the at least one TPG element with a metal.
 10. A method in accordance with claim 9, comprising plating the at least one TPG element with the metal selected from the group consisting of aluminum, copper, and combinations thereof.
 11. A method in accordance with claim 1, wherein the form is designed further contain at least one of fin features and complex details to reduce machining of the TPG-embedded heatsink.
 12. A method for forming an thermo pyrolytic graphite (TPG) therein according to a second embodiment of the present disclosure-embedded heatsink, the method comprising: obtaining a foam block; depositing at least one TPG element into the foam block; depositing the foam block with the at least one TPG element into a container; and filling the container with molding sand; and filling the foam block with a molten metal material.
 13. A method in accordance with claim 12, comprising depositing at least one planar TPG strip into the foam block.
 14. A method in accordance with claim 12, comprising filling the container with the molten metal material being selected from the group consisting of aluminum, copper, and combinations thereof.
 15. A method in accordance with claim 12, further comprising removing the metal block with the at least one TPG element embedded therein from the container.
 16. A method in accordance with claim 15, further comprising machining the metal block.
 17. A method for forming a thermo pyrolytic graphite (TPG) therein according to a third embodiment of the present disclosure-embedded heatsink, the method comprising: separating a foam block into at least two portions; depositing at least one TPG element between the at least two portions of the foam block; coupling the at least two portions of the foam block together to form a single block with the at least one TPG element; depositing the single block with the at least one TPG element into a container; and filling the container molding sand; and filling the foam block with a molten metal material.
 18. A method in accordance with claim 17, comprising depositing at least one planar TPG strip.
 19. A method in accordance with claim 17, coupling the at least two portions using an adhesive composition.
 20. A method in accordance with claim 17, comprising filling the container with the molten metal material being selected from the group consisting of aluminum, copper, and combinations thereof.
 21. A method in accordance with claim 17, further comprising removing the metal block with the at least one TPG element embedded therein from the container.
 22. The method as set forth in claim 21, further comprising machining the metal block. 